Method of forming phosphate coating on zinc

ABSTRACT

Disclosed is an improved method for coating a zinc surface comprising treating said surface with an aqueous, acidic solution containing: 
     (a) about 0.5 to about 4 percent phosphate ion; 
     (b) an ion selected from the group consisting of zinc ions, manganese ions, and mixtures thereof, said ions being present at a level sufficient to form dihydrogen phosphate with substantially all of said phosphate ions; and 
     (c) about 0.01 to about 1 percent complex fluoride ions; wherein the weight:weight ratio of complex fluoride ions:chloride ions in said solution is at a value of about 8:1 or greater. 
     It is preferred that the ratio complex of fluoride ion to chloride ion (F -  :Cl - ) in said solution to be maintained at a value of greater than about 8:1, preferably greater than about 10:1, and more preferably greater than about 14:1. The select weight:weight complex fluoride:chloride ratio substantially eliminates the abnormal crystal growth frequently found in treated surfaces while at the same time reduces the need for excess fluoride.

.Iadd.This reissue application is a continuation of reissue applicationNo. 07/209,113, filed Jun. 17, 1988, now abandoned, which is a reissueapplication No. 07/769,433, filed Aug. 26, 1985, now U.S. Pat. No.4,595,424.

The present invention relates to an improved method for formingadherent, corrosion resistant, deformation/paint base-protectivecoatings on zinc surfaces, and to materials for forming such coatings.The method is particularly useful for coating galvanized surfaces.

BACKGROUND OF THE INVENTION

Aqueous acidic solutions which are useful in forming phosphate coatingson zinc surfaces are well known. Certain of these solutions haveachieved widespread commercial use. Such solutions typically include thephosphate ion, the zinc or manganese ion and typically one or more ofthe following ions: nickel, cobalt, copper, nitrate, nitrite,fluoroborate or silicofluoride. The art has been able to form phosphatecoatings on zinc since about 1917, and there have been successivediscoveries of the effects of the nitrate, copper, nickel, fluoborate,and silicofluoride ions on the coating ability of such solutions madethrough the years. Presently, galvanized metal surfaces are effectivelyprovided with a deformation or paint base protective phosphate coatingby being treated in the following manner: (1) pre-treatment steps whichgenerally include a rinsing or cleaning step and an activation step; (2)a phosphate coating step; and (3) post-treatment steps including ageneral rinse step and a sealing rinse step. Such processes andsolutions for forming conversion coatings on metal surfaces are wellknown and have been described, for example, in Metal Handbook, VolumeII, 8th Edition, pages 529-547 of the American Society for Metals and inMetal Finishing Guidebook and Directory, pages 590-603 (1972), thecontents of both of which are specifically incorporated herein byreference. Despite the advances, the best present day formulations aretroublesome in certain respects.

For example, certain types of paint applied over the art-disclosedcoatings develop a roughness which is referred to as hazing, and thegloss is not of the highest order. Moreover, painted surfaces subjectedto bending do not resist flaking, cracking and the like to thecommercially desired degree.

Another problem associated with such coatings, particularly when theyare deposited on galvanized surfaces, is known as "white specking" or"nubbing". This phenomenon can best be described as uncontrolled crystalgrowth at pinpoint locations. This growth results in a flawed, roughsurface. The specks appear as large white growths; they are generallyzinc or zinc/iron phosphate crystals. While they can vary greatly insize, they are typically 50-150μ wide and 100-400μ high.

The larger crystal growths are apparent to the naked eye from virtuallyany angle. The smaller growths can only be seen with some magnification.However, when the treated or coated metal surface is painted, such flawsare immediately apparent and the resulting product is frequentlyunacceptable. A uniform paint film cannot be applied; this is truewhether the paint is applied by spray or electrodeposition. The "whitespecking" has been observed to occur during both the pre-treatment andtreatment stages. However, it most commonly appears during the treatmentstage.

There have been many attempts to effectively solve this problem ofcoating zinc surfaces, particularly galvanized surfaces; all suchattempts have focused on the treatment steps. Two of the most effectiveare disclosed in U.S. Pat. No. 3,240,633, issued Mar. 15, 1966, toGowman, et al., and U.S. Pat. No. 2,835,617, issued May 20, 1958, toMaurer; both of which are expressly incorporated herein by reference.These methods primarily involve the introduction of fluoride and ferricion into the bath.

These references clearly suggest that the use of fluoride ion in thetreatment bath assists in preventing the formation of "white specks" or"nubbing" under most conditions. However, it has also been observed thatthis method is not always effective in completely preventing theabnormal crystal growth, particularly when economical andenvironmentally sound levels of fluoride are used; the inclusion ofadditional fluoride being undesirable from both an economic andenvironmental standpoint.

It has now been discovered that while fluoride ion introduction has beenviewed as usually effective in preventing the abnormal crystal growth,it is in fact the presence of chloride ion which causes the "whitespecking" or "nubbing". Further, an increase in chloride ion without acorresponding increase in fluoride ion will increase the frequency andseverity of white specking. It will be appreciated that the artheretofore was wholly indiscriminate with regard to chloride level andthe ratio of chloride to fluoride.

It is commercially impractical if not impossible to remove all chlorideions from such processes. This is a result of the many sources of suchions, including, for example: reaction products of chlorateaccelerators, and other impurities; intentionally added salts such asthe ferric chloride as suggested in U.S. Pat. No. 3,240,633 (discussedabove); inert sodium chloride and other similar bulking or anti-cakingagents and additives; make-up water, and the like.

Accordingly, the present invention relates to a method for providing animproved phosphate coating on zinc surfaces. The improvement comprisesemploying solutions and baths with a select fluoride:chloride ratio.

SUMMARY OF THE INVENTION

The present invention relates to an improved method for coating a zincsurface comprising treating said surface with an aqueous, acidicsolution containing:

(a) about 0.5 to about 4 percent phosphate ion;

(b) an ion selected from the group consisting of zinc ions, manganeseions, and mixtures thereof, said ions being present at a levelsufficient to form dihyrogen phosphate with substantially all of saidphosphate ions; and

(c) about 0.01 to about 1 percent complex fluoride ions; wherein theweight:weight ratio of complex fluoride ions:chloride ions in saidsolution is at a value of about 8:1 or greater.

It is preferred that the ratio of complex fluoride ion to chloride ion(F⁻ :Cl⁻) in said solution to be maintained at a value of greater thanabout 8:1, preferably greater than about 10:1, and more preferablygreater than about 14:1. The select weight:weight complexfluoride:chloride ratio substantially eliminates the abnormal crystalgrowth frequently found in treated surfaces while at the same timereduces the need for excess fluoride.

DETAILED DESCRIPTION OF THE INVENTION

As will be appreciated from the above discussion, it has now beendiscovered that the "white specking" or "nabbing" imperfections presentin galvanized phosphate coatings are attributable to the presence ofcertain chloride levels in the coating solution. Accordingly, thepresent invention relates to a method which solves this problem,maximizing the effect of the fluoride while minimizing the ultimatelevel of fluoride employed. This solution is achieved by employing aselect complex fluoride ion:chloride ion ratio in the process. Lastly,it has been discovered that it is also desirable to employ low chloridelevels in all pre-treatment steps and in all pre-treatment agents. Thisprevents "white specking" from occurring in the pre-treat stages andfrom contaminating treatment bath with chloride ion carried over fromthe pre-treatment stage.

In the practice of the present invention, it is important to controlchloride level at the pre-treatment stage and the weight:weight ratio ofcomplex fluoride ion:chloride ion must be carefully controlled in thetreatment stage, i.e., the application of the improved deformation/paintbase protective phosphate coating itself.

Accordingly, the solutions employed in the treatment steps of thepresent invention for applying the improved phosphate coating areaqueous and acidic. They employ phosphate ions and generally compriseabout 0.5 percent to about 4 percent of the phosphate ions. Morepreferably, the phosphate is present at a level of about 0.5 to about2.5 percent, and still more preferably about 0.5 to about 2.0 percent.

The treatment solutions employed in the practice of the presentinvention for applying the improved phosphate coating also contain atleast one ion selected from the group consisting of zinc ions andmanganese ions. The selected zinc or manganese ion is preferablyemployed at a level at least sufficient to form dihydrogen phosphatewith the phosphate employed.

The treatment solutions employed in the practice of the presentinvention for applying the improved phosphate coating optionally containnitrate ions. Nitrate ions are preferably present at a level of about0.025 to about 2 percent, and more preferably about 0.05 to about 1percent. It will be appreciated that some level of nitrate ion will begenerated in the coating step of the present invention even if it is notadded. However, controlled addition is preferred.

The phosphate and nitrate discussed above may be added to or introducedinto the solution from any conventional source.

The treatment solutions employed in the practice of the presentinvention for applying the improved phosphate coating optionally containat least one ion selected from the group consisting of nickel ions andcobalt ions. In a preferred embodiment, the ion selected from this groupis employed at a level of about 0.01 percent to about 1 percent.

The nickel or cobalt ions may be introduced as salts such as thesulfate, phosphate, carbonate or nitrate salts, preferably as thecarbonate salt.

The treatment solutions employed in the practice of the presentinvention for applying the improved phosphate coating contain about 0.01to about 3 percent complex fluoride ion. More preferably, the complexfluoride ion is present at a level of about 0.025 to about 0.25 percent.It will be appreciated that the higher the ratio of zinc surface tosteel surface to be treated, the higher the desirable fluoride level.Thus, for example, when treating galvanized surfaces (greater than 50percent), levels of about 0.05 to about 0.2, and more preferably about0.075 to about 0.2, and still more preferably 0.08 to about 0.15, areemployed. These levels are preferably measured by employing a fluoridesensitive electrode such as one manufactured by Orion.

The complex fluoride ion may be added to or introduced into the solutionfrom any conventional source, including those discussed in U.S. Pat. No.2,835,617, issued to Maurer, on May 20, 1958, and U.S. Pat. No.3,240,633, issued to Gowman, et al., on Mar. 15, 1966, the disclosure ofboth being expressly incorporated herein by reference. While freefluoride ion may be employed under certain circumstances, it ispreferred that the fluoride ion be a complex (or complexed) fluorideion. In a highly preferred embodiment, the complex fluoride ion may beintroduced as silico fluoride. The silico fluoride ion providesespecially superior results when used on continuous hot dip zincsurfaces, and since they are readily available commercially and provideboth the necessary fluoride concentration and concurrently supply otherbeneficial ions, it may be, in many instances, much more desirable toformulate the compositions with silico fluoride as the startingmaterials rather than, for example, free fluoride ion sources such ashydrofluoric acid.

The solutions to be employed in the present invention maintain aweight:weight ratio of complex fluoride ion:chloride ion (F⁻(complex):Cl⁻) of greater than about 8:1, and more preferably about10:1. In a highly preferred embodiment, the solutions employed maintaina fluoride ion:chloride ion ratio of greater than about 14:1.

In order to effectively reduce the necessary level of fluoride ion, itis desirable that the treatment solutions of the present inventioncontain a maximum chloride ion level less than that which causes anynoticeable or observable interference with the application of a uniformcoating, i.e., "white specking" or "nubbing". In a highly preferredembodiment, the treatment solutions contain less than about 50 parts permillion chloride ion. This can be most efficiently accomplished bymaintaining a chloride level of less than about 0.0050 percent chlorideion in substantially all of the use solution employed in the practice ofthe present invention.

It will be appreciated from the above discussion that since it is thepresence of the chloride ion which interferes with the ultimate qualityof the coating, it is desirable to maintain a chloride ion level whichis as far below 50 ppm as is practical. This also reduces the necessarylevel of complex fluoride. Accordingly, it is preferred that thechloride level in the use solution be reduced to about 30 ppm or 0.003percent, and more preferably about 20 ppm or 0.002 percent. In a highlypreferred embodiment, the use solution is substantially free of chlorideions, i.e., contain less than about 15 ppm or 0.0015 percent.

The treatment solutions employed in the present invention for applyingthe improved phosphate coating optionally contain ferric (Fe⁺⁺⁺) ion. Ina preferred embodiment, the ferric ion is present at a level of at leastabout 0.0015. The ferric ion may be added to or introduced into thesolution from the workpiece or substrate, or from any conventionalsource; the ferric ion may be introduced into the solutions in the formof any of the conveniently available ferric salts which contain anionsthat are not detrimental to the coating forming ability of the solution.For example, this would include ferric acid phosphate, ferric nitrate,ferric fluoride, or ferric fluoborate. The source of ferric ion may alsobe introduced from the workpiece or part or added as a ferrous (Fe⁺⁺)salt or ferrous ion if an oxidizing agent is also added which willoxidize the ferrous ion to the ferric state, such as hydrogen peroxide,permanganate, nitrite, nitrate, etc.

It should be noted that ferrous chloride and ferric chloride may beemployed as the source of the ferric ion. However, as will beappreciated from the discussion of the chloride ion level and complexfluoride:chloride ratios that must be maintained in the practice of thepresent invention, the use of iron chlorides, or chloride salts of anyof the required or optional cations, must be vary carefully managed.

The preferred ferric ion concentration is a level of ferric ion whichapproaches or is at the saturation value.

It has been noted in the art that the incorporation of the ferric ion inthe aqueous acidic solutions such as those similar to the presentinvention is effective to substantially reduce the coating weight whichis obtained over a wide range of solution acidities. It has also beennoted by the art that solutions having total acid values in the range ofabout 10 to about 110 points are effective to form adherent protectivecoatings and are improved by the addition of the ferric ion. Points oftotal acid refers to the number of ml. of N/10 NaOH required to titratea 10 ml. sample of the solution to a phenolphthalein end point.

The solutions of this invention may be applied to the surface to becoated by spraying, roller coating, by atomizing the solution on apreliminarily heated zinc surface or by dipping the part to be coated ina tank containing the use solution. Solutions will form coatings in therange of about 110° F. to the boiling point of the solution but arepreferably operated in the range of about 130° F. to 180° F. with thebest overall results being obtained with solutions at about 150° F. forspray, roller coating, or atomizing, and 110°-130° F. for dipapplication.

As noted in the above discussion, the problem of white specking canoccur even during the pre-treatment stages if the chloride level is highenough. Further, if the chloride levels are high in the pretreatmentstage, the "carry-forward" of chloride ion into the treatment stage canresult in contamination of an otherwise acceptable treatment bath.Accordingly, this invention relates to a method for employingpre-treatment solutions and agents, such as cleaners, conditioners,activators, cleaner/conditioner combinations, and the like, whichcontain a level of chloride below which such chloride causes noticeableor observable interference with the application of a uniform coating. Ina preferred embodiment, pre-treatment solutions, agents, andreconstituted concentrates are substantially free of chloride ion. In ahighly preferred embodiment, such materials contain less than about 100ppm chloride ion, and more preferably less than about 50 ppm chlorideion.

For example, it is common in the art to employ a "conditioning rinse"which contains titanium phosphate in the coating of zinc surfaces. Suchconditioning rinses are frequently commercially prepared by theneutralization of titanium sulphate with caustic (NaOH), followed byphosphoric acid, etc. Because most commercial grade caustics containhigh chloride levels, the resulting conditioning rinses are extremelyhigh (frequently above 400 ppm) in chloride. Further, because theconditioning rinse frequently comes into direct contact with the surfacebeing treated in a somewhat concentrated form, the high chloride levelscause "white specking" or "nubbing".

In the practice of the present invention, therefore, it is preferredthat all concentrates, additives, replenishers, rinses, or combinationagents which perform two or more of these functions, and the like, beprepared, selected, or used in such a fashion that the combinationresults in the use solution possessing a chloride ion concentrationbelow which such chloride causes noticeable or observable interferencewith the application of a uniform coating.

In a highly preferrred embodiment, the methods of the present inventionemploy a titanium or high phosphate rinse solution having a chloride ionconcentration less than about 50 ppm chloride ion.

It may also be desirable and preferred to perform certain other selectsteps both prior to and after the application of the improved phosphatecoating. For example, it may be advantageous to take steps to see thatthe part or workpiece to be coated is substantially free of grease,dirt, particulate matter and the like by employing conventional cleaningprocedures and materials. These would include, for example, mild orstrong alkali cleaners, acidic cleaners, and the like. Such cleaners aregenerally followed and/or proceeded with a water rinse.

It has also been found to be advantageous to employ pre-treatmentsolutions following the cleaning steps such as that disclosed in U.S.Pat. Nos. 2,310,239, 2,874,081, and 2,884,351 (all of which areexpressly incorporated herein by reference) which pre-treatmentsolutions are of the general type which contain a condensed phosphateand a small quantity of the titanium or zirconium ion.

In a highly preferred embodiment, such materials and other pre-treatmentmaterials, possess a level of chloride ion below which such chloridecauses noticeable or observable interference with a uniform coating orare sufficiently rinsed from the part or workpiece so that high levelsof chloride ion are not introduced into the treatment solution nextemployed.

After the coating is formed by application of the solution of thisinvention, it is advantageous, particularly in those cases in which thecoated surface is to be subsequently painted, to rinse the coating in adilute aqueous chromic acid solution of conventional constituency, forexample, one containing about 0.025 to 0.1% chromium ion as Cr⁺³, Cr⁺⁶or mixtures thereof. Another class of useful rinses which may be appliedto the part or workpiece after the application of the coating aredisclosed in U.S. Pat. Nos. 3,975,214; 4,376,000; 4,457,790; 4,039,353;and 4,433,015, all of which are expressly incorporated herein byreference. In summary, the post-treatment compound placed into the rinseis a poly-4-vinyl-phenol or the reaction product of poly-4-vinyl-phenolwith an aldehyde or ketone.

After such a final chromic acid or poly-4-vinylphenol rinse, thecoatings have good resistance to corrosion prior to the application ofpaint and when painted have been found to be more resistant to cracking,chipping and peeling when the painted surface is deformed such as byforming to final desired shape in dies, by bending or the like.

Other art-disclosed treatments useful for effecting the formation of anadherent, uniform phosphate coating on metal surfaces may also beemployed in the processes of the present invention. See, for example,U.S. patent application Ser. No. 469,621 for "Improved Process forProducing Phosphate Coatings", filed Mar. 21, 1983.

By the term "substantially free of chloride ions" is meant that thepre-treatment material being described contains a chloride ionconcentration below that which the chloride ion noticeably or visuallyinterfere with a uniform phosphate coating by causing "white specking"during the pre-treatment steps or during the treatment itself.

The following examples are intended to illustrate the compositions andmethods of this invention in somewhat greater detail but it is to beunderstood the the particular ingredients, the proportions ofingredients, and the conditions of operation do not define the limits ofthis invention which have been set forth above. Percent concentrationthroughout this specification and claims refers to percentweight/volume, unless otherwise indicated.

EXAMPLE 1

Galvanized panels were processed using an immersion zinc phosphate bathin the cycle outlined. Chloride and fluoride were gradually introducedinto the zinc phosphate bath as solutions of "tap" water and sodiumchloride or sodium silica fluoride, respectively. The chloride level wasincreased until "white specking" was observed at which point fluoridewas then added until the white specking vanished. This cycle was thenrepeated using the previously altered zinc phosphate bath. To verifyresults, a fresh zinc phosphate bath was contaminated with an initialcharge of chloride greater than necessary to produce "white specking"and fluoride added until the "specking" had vanished. Panels were thenexamined for coating weight, crystal size and coating appearance.

    ______________________________________                                        Laboratory Process Cycle                                                      ______________________________________                                        Stage 1 - Alkaline Cleaner:                                                   Conventional 1/2 ounce per gallon                                             Cleaner                                                                       Concentration                                                                 Temperature  140° F.                                                   Time         120 seconds spray                                                Stage 2 - Warm Water Rinse:                                                   Temperature  Ambient                                                          Time         100 seconds spray                                                Stage 3 - Titanium-containing Surface Conditioner:                            Concentration                                                                              1.5 grams per liter; pH = 9.2; 15 p.p.m. Ti                      Temperature  Ambient                                                          Time         100 seconds Immersion                                            Chloride     less than 50 ppm                                                 concentration                                                                 Stage 4 - Zinc Phosphate Bath:                                                Concentration or                                                                           Free Acid - 1.0 points                                           Test         Total Acid - 20.0-22.0 points                                                 Accelerator - 3.0-3.5 points                                     Temperature  130° F.                                                   Time         240 seconds Immersion                                            Stage 5 - Cold Water Rinse:                                                   Temperature  Ambient                                                          Time         100 seconds Immersion                                            Stage 6 - Oven Dry:                                                           Temperature  250° F.                                                   Time         5 minutes                                                        ______________________________________                                    

                  TABLE 1                                                         ______________________________________                                        RESULTS                                                                       STAGE 4 BATH ANALYSIS                                                                                               F.sup.- :Cl.sup.-                       Sample     Specking  Chloride  Fluoride                                                                             Ratio                                   ______________________________________                                        Fresh      No        32     ppm  1000 ppm                                                                             31.3:1                                After      Slight    80     ppm  1100 ppm                                                                             13.8:1                                0.34 Grams NACl                                                               After      No        86     ppm  1400 ppm                                                                             16.3:1                                0.6 Grams Na.sub.2 SiF.sub.6                                                  After      Slight    108    ppm  1200 ppm                                                                             11.1:1                                0.2 Grams NaCl                                                                After      No        104    ppm  1400 ppm                                                                             13.5:1                                0.6 Grams Na.sub.2 SiF.sub.6                                                  Fresh      No        <10    ppm   900 ppm                                                                             --                                    After      Heavy     104    ppm   900 ppm                                                                              8.6:1                                0.8 Grams NaCl                                                                After      Slight    104    ppm  1000 ppm                                                                              9.6:1                                0.6 Grams Na.sub.2 SiF.sub.6                                                  After      No        98     ppm  1400 ppm                                                                             14.3:1                                3.34 Grams Na.sub.2 SiF.sub.6                                                 ______________________________________                                    

What is claimed is:
 1. An improved method for coating a zinc surfacecomprising treating said surface with an aqueous, acidic solutioncontaining:(a) about 0.5 to about 4 percent phosphate ion; (b) an ionselected from the group consisting of zinc ions, manganese ions, andmixtures thereof, said ions being present at a level sufficient to formdihydrogen phosphate with substantially all of said phosphate ions; and(c) about 0.01 to about 1 percent complex fluoride ions; and (d)measuring the chloride ion concentration and maintaining theweight:weight ratio of complex fluoride ions:chloride ions in saidsolution at a value of about 8:1 or greater.
 2. A method according toclaim 1, wherein said solution additionally contains about 0.025 toabout 2 percent nitrate ion.
 3. A method according to claim 1 whereinsaid solution additionally contains about 0.01 to about 1 percent of anion selected from the group consisting of cobalt ions, nickel ions, andmixtures thereof.
 4. A method according to claim 1, wherein the ratio ismaintained at a value of about 10:1 or greater.
 5. A method according toclaim 4 wherein the ratio is maintained at a value of about 14:1 orgreater.
 6. A method according to claim 1 wherein the phosphate ion ispresent at a level of about 0.5 to about 2.5 percent.
 7. A methodaccording to claim 4 wherein the phosphate ion is present at a level ofabout 0.5 to about 2.0 percent.
 8. A method according to claim 2 whereinthe nitrate ion is present at a level of about 0.05 to about 1 percent.9. A method according to claim 1 wherein the chloride ion is present ata level of less than about 0.0050 percent.
 10. A method according toclaim 9 wherein the chloride ion is present at a level of less thanabout 0.0020 percent.
 11. A method for coating a zinc surface comprisingtreating said surface with an aqueous acidic solution containing:(a)about 0.5 to about 4 percent phosphate ion; (b) about 0.025 to about 2percent nitrate ion; (c) an ion selected from the group consisting ofzinc ions, manganese ions, and mixtures thereof, said ions being presentat a level sufficient to form dihydrogen phosphate with substantiallyall of said phosphate ions; and (d) about 0.01 to about 1 percent of anion selected from the group consisting of cobalt ions, nickel ions, andmixtures thereof; wherein said solution contains less than about 0.0050percent chloride ion; and (e) measuring the chloride ion concentrationand maintaining the ratio of fluoride ions:chloride ions in saidsolution at a value of about 8:1 or greater.
 12. A method according toclaim 11 wherein the ratio is maintained at a value of about 10:1 orgreater.
 13. A method according to claim 12 wherein the ratio ismaintained at a value of about 14:1 or greater.
 14. A method accordingto claim 11 wherein the phosphate ion is present at a level of about 0.5to about 2.5 percent.
 15. A method according to claim 1 wherein allpre-treatment steps are substantially free of chloride ions. .Iadd. 16.A process for suppressing white specking when phosphate-coating a zincsurface, comprising:contacting the zinc surface with an aqueous, acidicsolution containing: (a) about 0.5 to about 4 percent phosphate ion; (b)an ion selected from the group consisting of zinc ions, manganese ions,and mixtures thereof; (c) about 0.01 to about 1 percent complex fluorideions; and (d) chloride ions; wherein the weight:weight ratio of complexfluoride ions:chloride ions in the solution is measured and maintainedduring coating at a value of about 8:1 or greater by adjusting theamount of complex fluoride ion in the composition thereby suppressingthe white specking. .Iaddend..Iadd.
 17. The process of claim 16 whereinthe weight ratio of complex fluoride ions:chloride ions in the solutionis maintained above about 10:1. .Iaddend..Iadd.18. The process of claim16 wherein the weight ratio of complex fluoride ions:chloride ions inthe solution is maintained above about 14:1. .Iaddend..Iadd.19. Theprocess of claim 16 wherein the solution contains manganese ions..Iaddend..Iadd.20. The process of claim 17 wherein the solution containsmanganese ions. .Iaddend..Iadd.21. The process of claim 18 wherein thesolution contains manganese ions. .Iaddend..Iadd.22. The process ofclaim 16 wherein the solution contains from about 0.025 to about 2percent of the solution of nitrate ions. .Iaddend..Iadd.23. The processof claim 17 wherein the solution contains from about 0.025 to about 2percent of the solution of nitrate ions. .Iaddend..Iadd.24. The processof claim 18 wherein the solution contains from about 0.025 to about 2percent of the solution of nitrate ions. .Iaddend..Iadd.25. The processof claim 18 wherein the solution contains from about 0.01 to about 1percent of the solution of an ion selected from the group consisting ofcobalt ions, nickel ions, and mixtures thereof. .Iaddend..Iadd.26. Theprocess of claim 17 wherein the solution contains from about 0.01 toabout 1 percent of the solution of an ion selected from the groupconsisting of cobalt ions, nickel ions, and mixtures thereof..Iaddend..Iadd.27. The process of claim 18 wherein the solution containsfrom about 0.01 to about 1 percent of the solution of an ion selectedfrom the group consisting of cobalt ions, nickel ions, and mixturesthereof. .Iaddend..Iadd.28. The process of claim 16 wherein the solutioncontains from about 0.5 to about 2.5 percent of phosphate ions..Iaddend..Iadd.29. The process of claim 17 wherein the solution containsfrom about 0.5 to about 2.5 percent of phosphate ions..Iaddend..Iadd.30. The process of claim 18 wherein the solution containsfrom about 0.5 to about 2.5 percent of phosphate ions..Iaddend..Iadd.31. The process of claim 16 wherein the solution containsless than about 0.005 percent of chloride ions. .Iaddend..Iadd.32. Theprocess of claim 17 wherein the solution contains less than about 0.005percent of chloride ions. .Iaddend..Iadd.33. The process of claim 18wherein the solution contains less than about 0.005 percent of chlorideions. .Iaddend..Iadd.34. The process of claim 22 wherein the solutioncontains from about 0.05 to about 1.0 percent nitrate ions..Iaddend..Iadd.35. The process of claim 23 wherein the solution containsfrom about 0.05 to about 1.0 percent nitrate ions. .Iaddend..Iadd.36.The process of claim 24 wherein the solution contains from about 0.05 toabout 1.0 percent nitrate ions. .Iaddend..Iadd.37. The process of claim28 wherein the solution contains from about 0.025 to about 2 percentnitrate ions. .Iaddend..Iadd.38. The process of claim 29 wherein thesolution contains from about 0.025 to about 2 percent nitrate ions..Iaddend..Iadd.39. The process of claim 30 wherein the solution containsfrom about 0.025 to about 2 percent nitrate ions. .Iaddend..Iadd.
 0. Theprocess of claim 37 wherein the solution contains from about 0.025 toabout 0.25 percent complex fluoride ions. .Iaddend..Iadd.41. The processof claim 38 wherein the solution contains from about 0.025 to about 0.25percent complex fluoride ions. .Iaddend..Iadd.42. The process of claim39 wherein the solution contains from about 0.025 to about 0.25 percentcomplex fluoride ions. .Iaddend..Iadd.43. The process of claim 37wherein the solution contains manganese ions. .Iaddend..Iadd.44. Theprocess of claim 38 wherein the solution contains manganese ions..Iaddend..Iadd.45. The process of claim 39 wherein the solution containsmanganese ions. .Iaddend..Iadd.46. The process of claim 37 wherein thesolution contains from about 0.025 to about 0.25 percent of complexfluoride ions. .Iaddend..Iadd.47. The process of claim 38 wherein thesolution contains from about 0.025 to about 0.25 percent of complexfluoride ions. .Iaddend..Iadd.48. The process of claim 39 wherein thesolution contains from about 0.025 to about 0.25 percent of complexfluoride ions. .Iaddend..Iadd.49. The process of claim 16 which furthercomprises contacting the zinc surface with at least one pretreatingsolution wherein the at least one pretreating solution contains lessthan about 0.01 percent chloride ions. .Iaddend..Iadd.50. In a methodfor phosphate-coating a zinc surface wherein the surface is contactedwith an aqueous, acidic solution, the improvement comprising:suppressingthe formation of white specking in said coating by contacting the zincsurface with an aqueous, acidic solution containing: (a) about 0.5 toabout 4 percent phosphate ion; (b) an ion selected from the groupconsisting of zinc ions, manganese ions, and mixtures thereof; (c) about0.01 to about 1 percent complex fluoride ions; and (d) chloride ions,wherein the weight:weight ration of complex fluoride ions:chloride ionsin the solution is at a value of about 8:1 or above; and maintainingsaid ratio at a value of about 8:1 or above during formation of thecoating by adjusting the amount of complex fluoride ion in the solutionthereby suppressing white specking. .Iaddend.